1. Field of the Invention
This invention generally relates to a method of, and an arrangement for, determining a condition of a sample to be analyzed and, more particularly, to the early and accurate diagnosis of heart and/or brain disease in human patients.
2. Description of the Related Art
Heart and brain disease are still the leading causes of death around the world. Conventional detection of such disease relies on electrocardiograph (EKG) and electroencephalograph (EEG) devices for measuring heart and brain wave activity by sensing electrical signals at various sites on the human body, and by recording these signals as waveforms. A cardiologist or a neurologist evaluates the EKG/EEG waveforms to determine abnormalities therein. Such evaluation requires considerable training and skill. Even despite a high degree of training and skill, an EKG/EEG waveform can still be interpreted as indicating normal heart/brain activity even in the presence of advanced coronary artery disease and brain epilepsy. Experience has shown that conventional EKG/EEG devices, although useful, are not sufficiently reliable to diagnose heart/brain disease, either due to insufficient sensitivity or specificity, and certainly not at an early stage of heart/brain disease. It has been estimated that over 50% of people with occlusive coronary artery disease or brain epilepsy have been reported to have normal EKG/EEG waveforms.
The prior art has proposed several approaches to extract more information from the EKG/EEG signals. U.S. Pat. No. 4,924,875 teaches the extraction of information regarding ischemia, propensity to ventricular tachycardia and other disorders in the heart which affect cardiac electrical activity. U.S. Pat. No. 4,579,125 teaches the determination of the frequency content of EEG signals from the brain. U.S. Pat. No. 4,421,122 teaches the topographic mapping of a person's brain.
In the EKG field, such functions as the frequency content of the EKG signals, e.g. power spectrum, and the amplitude histogram, e.g. occurrence frequency, have been analyzed. In the EEG field, such functions as the power spectrum, the coherence and the cross correlation have been considered. However, in each case, usually a small portion of one cycle of the processed EKG/EEG signal has been utilized. This has proven to be an unreliable diagnostic tool.
EKG/EEG signals arise from the discharge of electrical potentials from hundreds of thousands of electrically active cells, thereby resulting in a complex resultant signal. Isolated signal processing analysis of small portions of the processed EKG/EEG signal does not produce reliable data. The analysis of a single function characteristic of the EKG/EEG signal simply does not produce sufficient or reliable information. Conventional time and frequency domain analysis of the EKG/EEG signal, as well as the analysis of isolated minor portions of single functions of the EKG/EEG signal, fail to address information regarding non-linearities as well as cross correlation, coherence and phase angle over time. The joint effect of all these functions, particularly over an extended test period of many test cycles, has not been considered. As a result, the early and reliable detection of heart and brain disease, as well as the specific diagnosis of the type of heart disease, are not presently available, particularly at a time when the chronic disease might be treated and its progress retarded or halted.